Variable valve apparatus

ABSTRACT

An arm coupling mechanism for selectively switching a double valve variable control and single valve variable control. The single valve variable control is achieved in a condition in which a large lift arm and a second rocking cam arm are coupled together with a pin. The second rocking cam arm for moving a second valve includes a pin hole, in which the pin is inserted, formed therein. The position of the pin hole is set so that a pin switching operation can be executed when control is provided to achieve an operating angle, at which the single valve variable control is to be started for reduced NOx. A second driving cam is adapted to have a cam height greater than a cam height of a first driving cam.

TECHNICAL FIELD

The present invention relates to a variable valve apparatus and, more particularly, to a variable valve apparatus for an internal combustion engine capable of mechanically changing valve-opening characteristics of a valve.

BACKGROUND ART

Patent Document 1, for example, discloses a variable valve apparatus for an internal combustion engine capable of mechanically changing valve-opening characteristics of a valve. Fixed to a single camshaft in this variable valve apparatus are two rotary cams, a first rotary cam and a second rotary cam. Of two intake valves—a first intake valve and a second intake valve—disposed in a single cylinder, the first rotary cam drives to open or close the first intake valve and the second rotary cam drives to open or close the second intake valve. A variable valve transmission mechanism including a four-bar linkage is each disposed between the first rotary cam and the first intake valve and between the second rotary cam and the second intake valve.

The four-bar linkage of the variable valve transmission mechanism includes four major elements: an input arm, a transmission arm, a rocking arm, and a control arm. The input arm includes an input portion that abuts on the rotary cam. The transmission arm is rockably coupled to the input arm. The rocking arm, while being rockably coupled to the transmission arm, is rockable around a rotary control shaft so as to transmit a driving force transmitted from the rotary cam to an output portion that opens or closes the intake valve. The control arm, while being rotatably driven about the rotary control shaft, is rockably coupled to the input arm. Valve-opening characteristics of the intake valve can be mechanically changed by controlling a posture of the four-bar linkage to thereby change the position of the rotary cam relative to the input portion.

The conventional variable valve apparatus cited above further includes a selector mechanism for changing a method of controlling the valve-opening characteristics of the second intake valve from a variable control to a fixed control, or vice versa. More specifically, the variable valve apparatus includes a coupling mechanism that couples a four-bar linkage relating to the first intake valve (a first linkage) to a four-bar linkage relating to the second intake valve (a second linkage). The variable valve apparatus further includes another mechanism for holding the posture of the second linkage in a posture that results, when the coupling is disengaged, in an operating angle of the second intake valve becoming the maximum or minimum value. The coupling mechanism includes a through hole extended in the control arm in each of the four-bar linkages and a coupling pin inserted in the through hole. The mechanism for holding the posture of the second linkage when the coupling is disengaged includes a through hole extended in a fixing plate, a through hole extended in the control arm of the second linkage (a second control arm), and the above-referenced coupling pin.

The coupling pin is engaged with the through hole in the second control arm at all times. The coupling pin can move, while being left engaged with the through hole in the second control arm, toward the side of the control arm of the first linkage (a first control arm) or the side of the fixing plate. When the coupling pin moves toward the side of the first control arm and is inserted in the through hole in the first control arm, the second control arm is coupled to the first control arm through the coupling pin. When the first and second control arms are coupled together, the first linkage and the second linkage assume the same posture at all times. Accordingly, in this condition, the first and second valves can be controlled to exhibit the same valve-opening characteristics.

When the coupling pin moves toward the side of the fixing plate and is inserted in the through hole in the fixing plate, on the other hand, the second control arm is coupled to the fixing plate via the coupling pin. When the second control arm is coupled to the fixing plate, the second linkage is fixed to a predetermined posture. In this case, the posture of the first linkage is controlled so as to change the position of the rotary cam relative to the input portion. This allows the valve-opening characteristics of the first valve only to be mechanically changed with the valve-opening characteristics of the second valve fixed.

Specifically, according to the aforementioned variable valve apparatus, either one of two different control modes can be selectively executed, that is, having the same valve-opening characteristics for the first intake valve and the second intake valve (double valve variable control) or having different valve-opening characteristics between the first intake valve and the second intake valve (single valve variable control). As a result, changing the valve-opening characteristics between the first intake valve and the second intake valve, or in particular, changing a lift between the two valves varies an intake flow rate. This generates a swirl flow in a combustion chamber, thereby stabilizing combustion in the combustion chamber.

Including the above-mentioned document, the applicant is aware of the following document as a related art of the present invention.

[Patent Document 1] Japanese Patent Laid-open No. 2004-100555

DISCLOSURE OF INVENTION

In accordance with the related art mechanism, it is arranged that, when the double valve variable control is switched to the single valve variable control, the second linkage assumes temporarily the posture of achieving the maximum or minimum value for the operating angle of the second intake valve by way of the current operating angle. This approach means that it is necessary, when the control mode is switched between the double valve variable control and the single valve variable control, to control the operating angle in the current operating range to either the maximum or minimum value thereof. In addition, after a new control mode is selected, it becomes necessary to move the first intake valve, which is to be variable controlled, to a lift required for producing an effective difference in the intake flow rate between these intake valves.

As such, a certain amount of time is required for switching from the double valve variable control to the single valve variable control. Furthermore, upon the switching, it is also necessary to control an ignition timing and a fuel injection amount so as to prevent torque of the internal combustion engine from undergoing any sudden change. This could aggravate fuel economy. In the related art mechanism, however, no considerations are made in terms of shortening the switching operation time. There is still room for examination in the related art technique in this respect.

The present invention has been made to solve the above and it is an object of the present invention to provide a variable valve apparatus that allows valve-opening characteristics of a valve to be changed from variable control to fixed control, or vice versa, and that can achieve prompt switching operation between the two control modes.

The above object is achieved by a variable valve apparatus in which control on valve-opening characteristics of at least one valve to be switched of a plurality of valves is changed from that under a variable control mode to that under a fixed control mode or vice versa. The variable valve apparatus includes a rocking member interposed between a main cam and the valve, the rocking member transmitting a pressing force of the main cam to the valve. A valve-opening characteristics variable means for controlling a posture of the rocking member within a predetermined range to variably control valve-opening characteristics of the valve to be switched is provided. A valve-opening characteristics fixing means for fixedly controlling the valve-opening characteristics of the valve to be switched is further provided. A changing means for switching control on the valve-opening characteristics of the valve to be switched from that under the variable control mode to that under the fixed control mode or vice versa is further provided. The changing means are arranged so as to allow the valve-opening characteristics of the valve to be switched to be changed in a posture of the rocking member associated with an operating range requiring a switch of the valve-opening characteristics of the valve to be switched.

In a second aspect of the present invention, the operating range requiring a switch of the valve-opening characteristics of the valve to be switched according to the first aspect of the present invention may include a low engine speed range or a light load range intended for reduced NOx or improved fuel economy.

In a third aspect of the present invention, the valve-opening characteristics variable means may include an intermediate member disposed between the main cam and the valve to be switched and control means for changing a position of the intermediate member. The intermediate member may be shared among the plurality of valves including the valve to be switched. A second cam that is separate from the main cam may also be provided. The valve-opening characteristics fixing means may include an input arm that rocks in phase with rotation of the second cam. The changing means may engage or disengage coupling between the rocking member for moving the valve to be switched and the input arm. The second cam may be arranged to have a greater cam height than the main cam.

In a fourth aspect of the present invention, the changing means may be arranged such that, when the operating range requiring a switch of the valve-opening characteristics of the valve to be switched exists over a predetermined range, the valve-opening characteristics of the valve to be switched can be switched with the rocking member in a posture that achieves the minimum operating angle and/or lift of the valve to be switched within the predetermined range.

In a fifth aspect of the present invention, the changing means may be arranged such that, when the operating range requiring a switch of the valve-opening characteristics of the valve to be switched exists over a predetermined range, the valve-opening characteristics of the valve to be switched can be switched with the rocking member in a posture that achieves the maximum operating angle and/or lift of the valve to be switched within the predetermined range.

In a sixth aspect of the present invention, the valve-opening characteristics variable means may include an intermediate member disposed between the main cam and the valve to be switched and control means for changing a position of the intermediate member. The intermediate member may be shared among the plurality of valves including the valve to be switched. A second cam that is separate from the main cam may also be provided. The valve-opening characteristics fixing means may include an input arm that rocks in phase with rotation of the second cam. The changing means may include a pin, the changing means engaging or disengaging coupling of the pin between the rocking member for moving the valve to be switched and the input arm. Either the rocking member for moving the valve to be switched or the input arm may include a pin hole, in which the pin is inserted. An entrance portion of the pin hole may include a guide surface formed for guiding the pin being inserted into, or moved out of, the pin hole.

In a seventh aspect of the present invention, the guide surface may have an inclined angle relative to an axis of the pin hole, the angle becoming smaller toward the entrance portion of the pin hole.

In a eighth aspect of the present invention, a profile of the second cam may be arranged such that the second cam achieves a phase of the valve to be switched different from a valve phase achieved by the main cam.

According to a first aspect of the present invention, time required for the switching operation can be effectively shortened as compared with a case, in which switching is done at the maximum or minimum value in the variable range of the valve-opening characteristics of the valve to be switched.

If switching is done at the maximum or minimum value in the variable range of the valve-opening characteristics of the valve to be switched when an operating range requiring a switch in the valve-opening characteristics of the valve to be switched is a low engine speed range or a light load range with the aim of reduced NOx or improved fuel economy, the time required for the switching operation will be longer. According to the second aspect of the present invention, such an operation time can be effectively shortened.

If the intermediate member is shared among a plurality of valves including the valve to be switched and if the main cam is selected as the driving cam, these valves are driven by the main cam to offer the same valve-opening characteristics. Assume, in such a case, that an attempt is made to switch the valve-opening characteristics of the valve to be switched with the rocking member in a posture for the operating range that requires a switch in the valve-opening characteristics of the valve to be switched. If the second cam has the same cam height as the main cam in this case, it becomes impossible to control the lift of the valve to be switched driven by the second cam to a value greater than the lift of the other valves driven by the main cam. According to the third aspect of the present invention, on the other hand, the upper limit value of the lift of the valve to be switched to be controlled by the second cam is not affected by the presence of the intermediate member. It is then possible to switch the valve-opening characteristics of the valve to be switched with the rocking member in a posture for the desired operating range.

According to the third aspect of the present invention, the lift of the valve to be switched can be instantaneously changed to the large lift upon completion of the switching operation. In addition, according to the fourth aspect of the present invention, the operation time for controlling the variably controlled other valves to a sufficiently small lift after the completion of the switching operation can be further shortened.

According to the fifth aspect of the present invention, at any time after the valve-opening characteristics of the valve to be switched have been changed to the fixed control, the valves other than the valve to be switched are varied in a range with a smaller operating angle or lift than that of the valve to be switched in the predetermined range according to the fifth aspect of the present invention. This prevents a gap from being produced between the second cam and the input arm. As a result, noise or impact load can be prevented from occurring between the second cam and the input arm during the lift operation.

According to the sixth aspect of the present invention, even with the pin axially misaligned with the pin hole, the rocking member rotates as the pin is guided by the guide surface, bringing the pin into axial alignment with the pin hole. This achieves coupling of the pin. As a result, according to the present invention, the operation time required for the switching operation can be effectively shortened.

According to the seventh aspect of the present invention, the speed, at which the rocking member moves when coupling of the pin is disengaged, can be decelerated. Accordingly, according to the present invention, noise or impact load that would otherwise occur from a contact between members during disengagement of the coupling of the pin can be prevented.

According to the eighth aspect of the present invention, valve-opening phases of the valve to be switched driven by the second cam and the other valves driven by the main cam can be varied without using any mechanism for changing the phase of the valve.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a view for illustrating a mechanism interposed between a driving cam and a valve in a variable valve apparatus according to a first embodiment of the present invention.

FIG. 2 is a view showing a variable valve mechanism shown in FIG. 1, as viewed from an axial direction of the camshaft.

FIG. 3 is an exploded perspective view showing the variable valve mechanism and the fixed valve mechanism shown in FIG. 1.

FIGS. 4(A) and 4(B) are views for illustrating setting of the position of the pin hole in the variable valve apparatus shown in FIG. 1.

FIG. 5 is a view for illustrating the arrangement of a variable valve apparatus according to the second embodiment of the present invention.

FIG. 6 is a diagram showing valve-opening characteristics of a valve achieved by the variable valve apparatus.

FIG. 7 is a view for illustrating a modified example of the arrangement of a variable valve apparatus according to the second embodiment of the present invention.

FIG. 8 is a diagram showing valve-opening characteristics of a valve achieved by the variable valve apparatus.

FIG. 9 shows a torque curve diagram for illustrating the operating range, in which the single valve variable control is executed, in the variable valve apparatus according to the third embodiment of the present invention.

FIGS. 10(A) and 10(B) are views for illustrating problems as they are posed when the pin switching operation is performed on the side of the small operating angle of the range, over which the single valve variable control is executed.

FIGS. 11(A) and 11(B) are views for illustrating operations when the setting is made for pin switching operation according to the third embodiment of the present invention.

FIG. 12 is a view for illustrating the arrangement of a variable valve apparatus according to the fourth embodiment of the present invention.

FIG. 13 is a cross-sectional view for illustrating the arrangement specific to the arm coupling mechanism according to the fourth embodiment of the present invention.

FIGS. 14(A) and 14(B) are enlarged views showing the portion A of FIG. 13.

FIGS. 15(A) and 15(B) are views for illustrating pin switching operations in the fourth embodiment of the present invention.

FIG. 16 is a view for illustrating the operation of the second rocking cam arm during the pin switching operation.

FIG. 17 is enlarged views showing the portion A of FIG. 13.

BEST MODE FOR CARRYING OUT THE INVENTION First Embodiment [Configuration of a Variable Valve Apparatus]

FIG. 1 is a view for illustrating a mechanism interposed between a driving cam and a valve in a variable valve apparatus 1 according to a first embodiment of the present invention. It is assumed herein that each of the cylinders of the internal combustion engine has two intake valves and two exhaust valves. The arrangement shown in FIG. 1 functions as a mechanism for driving two intake valves or two exhaust valves disposed in a single cylinder.

Referring to FIG. 1, a camshaft 10 of the variable valve apparatus 1 is provided with two driving cams 12, 14 per cylinder. Two valves—a first valve 16L and a second valve 16R—are symmetrically disposed with respect to one of the two driving cams (a first driving cam) 12. Each of variable valve mechanism 20L, 20R is disposed between the first driving cam 12 and each of the valves 16L, 16R. The variable valve mechanism 20L, 20R operatively couple a lifting movement of each of the valves 16L, 16R to a rotational movement of the first driving cam 12.

The other of the two driving cams (a second driving cam 14) is disposed such that the second valve 16R is sandwiched between the first driving cam 12 and the second driving cam 14. A fixed valve mechanism 30 is disposed between the second driving cam 14 and the second valve 16R. The fixed valve mechanism 30 operatively couples a lifting movement of the second valve 16R to a rotational movement of the second driving cam 14. The variable valve apparatus 1 is arranged so that an element, to which the lift movement of the second valve 16R is coupled, can be selected between the variable valve mechanism 20R and the fixed valve mechanism 30.

(1) Detailed Configuration of Variable Valve Mechanism

Referring first to FIG. 2, the arrangement of the variable valve mechanism 20L, 20R will be described in detail. FIG. 2 is a view showing a variable valve mechanism 20 shown in FIG. 1, as viewed from an axial direction of the camshaft 10. The left and right variable valve mechanism 20L, 20R will herein be described without discriminating one from the other, since the left and right variable valve mechanism 20L, 20R are basically symmetrical relative to the first driving cam 12. When the left variable valve mechanism 20L is not differentiated from the right variable valve mechanism 20R in this specification and its accompanying drawings, the mechanism will be simply referred to as the variable valve mechanism 20. Similarly, each of the components of the variable valve mechanism 20L, 20R and parts that are symmetrically disposed including the valves 16L, 16R will be referred to simply as one without appended with the symbol of L or R unless it is otherwise necessary to differentiate one on the left from the other on the right.

Referring to FIG. 2, in the variable valve apparatus 1, a rocker arm 32 is supported by the valve 16. The variable valve mechanism 20 is interposed between the first driving cam 12 and the rocker arm 32, continuously changing an operative coupling condition between the rotational movement of the first driving cam 12 and a rocking movement of the rocker arm 32.

As will be described in the following, the variable valve mechanism 20 includes, as major components thereof, a control shaft 34, a control arm 36, a link arm 38, a rocking cam arm 40, a first roller 42, and a second roller 44. The control shaft 34 is disposed, extending in parallel with the camshaft 10. The angle of rotation of the control shaft 34 can be controlled to any arbitrary value by an mechanism (e.g., a motor or the like) not shown.

The control arm 36 is fixed integrally with the control shaft 34 using a bolt 46 (see FIG. 1). The control arm 36 protrudes from the control shaft 34 in the diametric direction. The link arm 38 of an arcuate shape is mounted on this protrusion. A trailing end portion of the link arm 38 is coupled rotatably to the control arm 36 using a pin 48. The pin 48 is eccentric from a center of the control shaft 34, serving as a fulcrum of rocking motion of the link arm 38.

The rocking cam arm 40, rockably supported on the control shaft 34, is disposed such that a leading end thereof is oriented toward an upstream side in the direction of rotation of the first driving cam 12. The rocking cam arm 40 includes a slide surface 50 formed on a side thereof opposing the first driving cam 12. The slide surface 50 contacts the second roller 44. The slide surface 50 is formed into a curved surface such that the spacing from the first driving cam 12 gradually narrows as the second roller 44 moves from the leading end side of the rocking cam arm 40 toward an axial center of the control shaft 34. A rocking cam surface 52 is formed on a side of the rocking cam arm 40 opposite the slide surface 50. The rocking cam surface 52 includes a non-acting face 52 a and an acting face 52 b. The non-acting face 52 a is formed with a constant distance from the center of rocking of the rocking cam arm 40. The acting face 52 b is formed such that the distance from the axial center of the control shaft 34 becomes greater as the acting face 52 b is away from the non-acting face 52 a.

The first roller 42 and the second roller 44 are disposed between the slide surface 50 of the rocking cam arm 40 and a peripheral surface of the first driving cam 12. More specifically, the first roller 42 is disposed so as to be in contact with the peripheral surface of the first driving cam 12, while the second roller 44 is disposed so as to be in contact with the slide surface 50 of the rocking cam arm 40. Both the first roller 42 and the second roller 44 are supported rotatably on a coupling shaft 54 secured to a leading end portion of the aforementioned link arm 38. The link arm 38 can pivots about the pin 48. Accordingly, the first and second rollers 42, 44 can rock along the slide surface 50 and the peripheral surface of the first driving cam 12, respectively, while keeping a predetermined distance from the pin 48.

A lost motion spring not shown is hooked onto the rocking cam arm 40. The lost motion spring is a compression spring. An urging force from the lost motion spring acts as an urging force allowing the slide surface 50 to urge the second roller 44 and pressing the first roller 42 against the first driving cam 12. As a result, the first roller 42 and the second roller 44 are positioned correctly by being sandwiched from both sides between the slide surface 50 and the peripheral surface of the first driving cam 12. The lost motion spring is not limited to the compression spring; rather the spring may, for example, be a torsion spring.

The above-referenced rocker arm 32 is disposed downward of the rocking cam arm 40. The rocker arm 32 includes a rocker roller 56 disposed so as to oppose the rocking cam surface 52. The rocker roller 56 is rotatably mounted at a middle portion of the rocker arm 32. The rocker arm 32 has a first end supported by a valve stem 58 of the valve 16. The rocker arm 32 also has a second end supported rotatably by a hydraulic lash adjuster 60. In a lift operation, the valve stem 58 is urged in a closing direction, i.e., a direction of pushing up the rocker arm 32 by a valve spring not shown. Further, the rocker roller 56 is pressed against the rocking cam surface 52 of the rocking cam arm 40 by this urging force and the hydraulic lash adjuster 60.

In accordance with the arrangements of the variable valve mechanism 20, as the first driving cam 12 rotates, a pressing force of the first driving cam 12 is transmitted to the slide surface 50 via the first roller 42 and the second roller 44. As a result, a point of contact between the rocking cam surface 52 and the rocker roller 56 shifts from the non-acting face 52 a to the acting face 52 b, This in turn pushes down the rocker arm 32, opening the valve 16.

Further, in accordance with the arrangements of the variable valve mechanism 20, changing the angle of rotation of the control shaft 34 changes the position of the second roller 44 on the slide surface 50. This varies a rocking range of the rocking cam arm 40 in the lift operation. More specifically, when the control shaft 34 is rotated counterclockwise as seen in FIG. 2, the second roller 44 on the slide surface 50 moves toward the leading end side of the rocking cam arm 40. The angle, through which the rocking cam arm 40 needs to be rotated for the period of time that begins when the rocking cam arm 40 starts its rocking motion as a result of the pressing force of the first driving cam 12 being transmitted and ends when an actual pressure acting on the rocker arm 32 begins, becomes greater with increased angles of counterclockwise rotation of the control shaft 34 as seen in FIG. 2. Specifically, according to the variable valve mechanism 20, rotating the control shaft 34 counterclockwise as seen in FIG. 2 makes small the operating angle and the lift of the valve 16. Rotating the control shaft 34 clockwise as seen in FIG. 2, on the other hand, allows the operating angle and the lift of the valve 16 to be made greater.

(2) Detailed Configuration of Fixed Valve Mechanism

The fixed valve mechanism 30 will be described below in detail with reference to FIG. 3 in addition to FIG. 1.

Referring to FIG. 1, the fixed valve mechanism 30 is interposed between the second driving cam 14 and a second rocking cam arm 40R. The fixed valve mechanism 30 operatively couples a rocking movement of the second rocking cam arm 40R to a rotational movement of the second driving cam 14. The fixed valve mechanism 30 includes a large lift arm 70 and an arm coupling mechanism 72 (see FIG. 3). The large lift arm 70 is driven by the second driving cam 14. The arm coupling mechanism 72 couples the large lift arm 70 to the second rocking cam arm 40R.

The large lift arm 70 is disposed in juxtaposition with the second rocking cam arm 40R on the control shaft 34. The large lift arm 70 is rotatable independently of the second rocking cam arm 40R. An input roller 74 is rotatably supported on the large lift arm 70. The input roller 74 contacts a peripheral surface of the second driving cam 14. A lost motion spring not shown is hooked onto the large lift arm 70. A spring force of the lost motion spring acts as an urging force that presses the input roller 74 up against the peripheral surface of the second driving cam 14.

FIG. 3 is an exploded perspective view showing the variable valve mechanism 20 and the fixed valve mechanism 30 shown in FIG. 1. Referring to FIG. 3, the large lift arm 70 includes a pin 76 that can be advanced toward, and retracted from, the second rocking cam arm 40R. The large lift arm 70 also includes a hydraulic chamber 78 formed therein. The hydraulic chamber 78 has an opening on the side of the second rocking cam arm 40R. The pin 76 is fitted into the hydraulic chamber 78. Hydraulic oil is supplied to the hydraulic chamber 78 through a hydraulic path not shown. When a hydraulic pressure in the hydraulic chamber 78 is boosted through the arrangement as described above, the pin 76 is designed to be pushed out of the hydraulic chamber 78 toward the second rocking cam arm 40R by the hydraulic pressure.

The second rocking cam arm 40R, on the other hand, includes a pin hole 80 formed therein. The pin hole 80 has an opening on the side of the large lift arm 70. The pin 76 and the pin hole 80 are disposed on the same circular arc about the control shaft 34. This arrangement results in the following. Specifically, when the second rocking cam arm 40R is positioned at a predetermined angle of rotation relative to the large lift arm 70, the pin hole 80 is aligned with the pin 76. A return spring 82 and a piston 84 are disposed inside the pin hole 80 in that order from the rear.

In accordance with the abovementioned arrangements, when the pin hole 80 is aligned with the pin 76, the pin 76 abuts on the piston 84. If the force of the hydraulic pressure of the hydraulic chamber 78 pushing the pin 76 is greater at this time than the force of the return spring 82 pushing the piston 84, the pin 76 advances into the pin hole 80 as if it pushed the piston 84 into the pin hole 80. When the pin 76 is inserted into the pin hole 80, the second rocking cam arm 40R and the large lift arm 70 are coupled together via the pin 76. Specifically, the pin 76, the hydraulic chamber 78 supplied with the hydraulic oil, the pin hole 80, the return spring 82, and the piston 84 make up the arm coupling mechanism 72.

It is arranged in the variable valve apparatus 1 that the pin 76 and the pin hole 80 are aligned with each other when the second rocking cam arm 40R is positioned at a predetermined angle of rotation relative to the large lift arm 70. When the pin 76 is correctly aligned with the pin hole 80, the pin 76 is inserted into the pin hole 80, causing the large lift arm 70 to be coupled with the second rocking cam arm 40R. In the variable valve apparatus 1, the element, to which the lift movement of the second valve 16R is operatively coupled, can be switched from the variable valve mechanism 20R to the fixed valve mechanism 30 by using the arm coupling mechanism 72 to couple the large lift arm 70 to the second rocking cam arm 40R. Conversely, the element, to which the lift movement of the second valve 16R is operatively coupled, can be switched from the fixed valve mechanism 30 to the variable valve mechanism 20R by disengaging the coupling achieved by the arm coupling mechanism 72 between the large lift arm 70 and the second rocking cam arm 40R.

When the large lift arm 70 and the second rocking cam arm 40R are not coupled together, the rotational movement of the camshaft 10 is transmitted from the first driving cam 12 to each slide surface 50 of a first rocking cam arm 40L and the second rocking cam arm 40R via the first roller 42 and the second roller 44. Accordingly, in this case, control can be provided such that the operating angle and the lift of the first valve 16L exhibit the same characteristics as those of the second valve 16R through operative coupling to the rotation of the control shaft 34 (double valve variable control).

When the large lift arm 70 and the second rocking cam arm 40R are coupled together, on the other hand, the rotational movement of the camshaft 10 is transmitted from the second driving cam 14 to the second rocking cam arm 40R via the large lift arm 70. The large lift arm 70 and the second rocking cam arm 40R are coupled together in a condition, in which the control shaft 34 is rotated to move a second roller 44R on a slide surface 50R to a position to be described later with reference to FIG. 4. As a result, the valve-opening characteristics of the second valve 16R are mechanically defined by the shape and positional relationship of the second driving cam 14, the large lift arm 70, and the second rocking cam arm 40R. The valve-opening characteristics of the second valve 16R are thereby fixed and constant regardless of the angle of rotation of the control shaft 34. The rotational movement of the camshaft 10 is transmitted to the first rocking cam arm 40L, on the other hand, from the first driving cam 12 via the first roller 42 and the second roller 44L. Accordingly, in this case, the valve-opening characteristics of the first valve 16L vary in association with to the angle of rotation of the control shaft 34, in the same manner as when the large lift arm 70 and the second rocking cam arm 40R are not coupled together.

As described in the foregoing, in accordance with the variable valve apparatus 1, the valve-opening characteristics of only the first valve 16L can be variably controlled (single valve variable control) when the large lift arm 70 and the second rocking cam arm 40R are coupled together. The variable valve apparatus 1 allows both the lift and the operating angle of the valve 16 to be continuously varied as described in the foregoing. Throughout this specification hereunder, the “lift and operating angle” of the valve 16 may be simply referred to as the “operating angle” or “lift” of the valve 16 unless otherwise specified.

(3) Setting of Pin Hole Position and Cam Profile in the First Embodiment

FIGS. 4(A) and 4(B) are views for illustrating setting of the position of the pin hole 80 in the variable valve apparatus 1 shown in FIG. 1. More specifically, FIG. 4(A) is a view showing setting of the position of a pin hole in a variable valve apparatus A to be referred to for comparison with the variable valve apparatus 1 according to the first embodiment of the present invention. FIG. 4(B) is a view showing setting of the position of the pin hole 80 in the variable valve apparatus 1 according to the first embodiment of the present invention. It is assumed that the variable valve apparatus A to be referred to for comparison has the same arrangements as those of the variable valve apparatus 1 according to the first embodiment of the present invention, except for the setting of the pin hole position and cam height of the second driving cam. A point of contact between the rocker roller 56 and the second rocking cam arm 40R will herein be referred to as “roller contact point X” and a point of boundary between the non-acting face 52 a and the acting face 52 b of the second rocking cam arm 40R will be referred to as “lift start point Y.” In addition, the angle formed between a straight line connecting a center of rotation P of the second rocking cam arm 40R and a center of rotation Q of the rocker roller 56, and a straight line connecting the center of rotation P and the lift start point Y will be referred to as “arm angle θ.”

From the viewpoint of productivity in manufacturing the camshaft 10 provided with the first driving cam 12 and the second driving cam 14, it is preferable that the first driving cam 12 have the same cam profile as the second driving cam 14. In the variable valve apparatus A shown in FIG. 4(A), the first driving cam and the second driving cam are arranged to have the same cam profile. In the variable valve apparatus A, regardless of whether the control mode is double valve variable control or single valve variable control, the second roller on the side of the second rocking cam arm tries to transmit the pressing force of the first driving cam to the slide surface of the second rocking cam arm. Accordingly, if the pin hole position is set such that the lift achieved by the fixed valve mechanism is smaller than the maximum lift variably achieved by the variable valve mechanism, with the first driving cam and the second driving cam being arranged to have the same cam height, the valve driven by the variable valve mechanism will be further driven by the variable valve mechanism after the maximum lift has been reached. As a result, single valve variable control is disabled.

Accordingly, in order to control the operating angle of the second valve on the fixed side independently, while achieving the maximum variable range for the operating angle by the variable valve mechanism in single valve variable control, it is necessary to set the pin hole position such that the posture of the second rocking cam arm achieves the maximum operating angle or more of the variable range obtained by the variable valve mechanism. The variable valve apparatus A shown in FIG. 4(A) represents the setting of the pin hole position that takes into account the above-cited considerations.

More specifically, FIG. 4(A) shows a condition, in which the pressing force of the driving cam does not act on the second rocking cam arm. FIG. 4(A) also shows a condition, in which the posture of the second rocking cam arm is controlled by the control shaft so as to achieve the maximum operating angle. In the variable valve apparatus A, the position of the pin hole in the second rocking cam arm is set such that, when the second rocking cam arm assumes a posture as that described above, the pin is aligned with the pin hole. The arm angle θ in this condition will be referred to as θ1. Setting the pin hole position through the foregoing way allows an even more effective swirl flow to be formed, since the difference in the lift between two valves is substantially enlarged.

In the variable valve apparatus 1 according to the first embodiment of the present invention, on the other hand, the position of the pin hole 80 is determined by taking into account the following considerations. Specifically, in an internal combustion engine, a request may be issued for single valve variable control in order to generate an effective swirl flow in the combustion chamber with an ultimate goal of a reduced amount of NOx exhausts in, for example, a light load operating range or a low engine speed range, in which the operating angle of the valve 16 is about 100 to 200° C.A. Similarly, in the internal combustion engine, a request may be issued for single valve variable control in the light load operating range or the low engine speed range with an ultimate goal, for example, of improved fuel economy. Upon receipt of such a request, in the internal combustion engine, the range, in which the double valve variable control is switched to the single valve variable control, is set to a predetermined low engine speed range or light load operating range with the aim of reduced NOx or improved fuel economy as an index.

In the variable valve apparatus 1 according to the first embodiment of the present invention, the position of the pin hole 80 on the second rocking cam arm 40R is set so as to meet the following condition. Specifically, referring to FIG. 4(B), the pin 76 should be aligned with the pin hole 80 in a condition, in which the arm angle θ is an angle θ2 which is larger than the abovementioned angle θ1, or to state it another way, in a condition, in which the posture of the second rocking cam arm 40R is controlled by the control shaft 34 so that the arm angle θ is an operating angle in the middle of the variable range of the valve 16 the variable valve mechanism 20 has. In other words, the position of the pin hole 80 is set such that, when the second rocking cam arm 40R is in a posture that achieves an operating angle for the operating range required for the switching operation from the double valve variable control to the single valve variable control (hereinafter may at times be referred to simply as “pin switching operation”), such a pin switching operation can be executed.

More specifically, in accordance with the first embodiment of the present invention, the position of the pin hole 80 is set such that the pin switching operation can be executed when the operating angle is controlled to fall within the range of about 100 to 200° C.A, i.e. when the operating angle is controlled to one for starting the single valve variable control in order to reduce NOx or for related purposes. Further, the position of the pin hole 80 is set such that the pin switching operation can be executed on the side of the smallest operating angle (in the below case, when the second rocking cam arm 40R assumes a posture that results in the operating angle being 100° C.A) of the range requiring the pin switching operation (e.g., a range that results in the operating angle falling within about 100 to 200° C.A).

In the variable valve apparatus 1 according to the first embodiment of the present invention, the profiles of the first driving cam 12 and the second driving cam 14 are set so that the cam height of the second driving cam 14 is greater than that of the first driving cam 12, as shown in FIG. 4(B). Specifically, it is arranged that the second driving cam 14 has a cam height such that the operating angle of the second valve 16R becomes a value equal to or more than the maximum value of the operating angle of the first valve 16L driven by the variable valve mechanism 20 when the pin is coupled.

The pin switching operation described above is executed to follow the steps given below. Specifically, it takes an operation time T1, during which the control shaft 34 is driven for change of an operating angle posture of the second rocking cam arm 40R in the current operating condition of the internal combustion engine to an operating angle posture that allows the pin hole 80 to be aligned with the pin 76. When the pin switching operation is completed and the second rocking cam arm 40R is coupled to the large lift arm 70, the lift movement of the second valve 16R is immediately switched to the operation by the fixed valve mechanism 30. For the first valve 16L driven by the variable valve mechanism 20, however, an operation time T2 is required after the pin switching operation has been completed. During this period of T2, the first rocking cam arm 40L is moved to achieve a small operating angle posture that enables generation of a desired swirl flow.

In accordance with the arrangement of the variable valve apparatus 1 according to the first embodiment of the present invention, the pin switching operation is executed when the second rocking cam arm 40R assumes an operating angle posture requiring the pin switching operation as described in the foregoing. Accordingly, the operation time T1 can be shortened as compared with that in the variable valve apparatus A (shown in FIG. 4(A)), in which the pin hole position is set to the maximum value of the operating angle variable range according to the variable valve mechanism 20. In the variable valve apparatus 1, it is arranged so that the second driving cam 14 has a cam height greater than that of the first driving cam 12. This allows the operating angle of the second valve 16R driven to achieve a constant value in the single valve variable control to be set to a value equal to or greater than the maximum lift to be achieved by the variable valve mechanism 20. Additionally, in accordance with the first preferred embodiment of the present invention, an approach is taken to vary the cam height between the first driving cam 12 and the second driving cam 14, thereby achieving the characteristics of the second valve 16R as described above. This allows the operating angle of the second valve 16R to be instantaneously changed to the desired large one upon completion of the pin switching operation.

As described earlier, the operation time T2 is required after the pin has been coupled in position, during which the first rocking cam arm 40L is moved from the operating angle posture, in which the pin coupling operation is performed, to the small operating angle posture that enables generation of the desired swirl flow. As compared with the variable valve apparatus A (shown in FIG. 4(A)), in which the pin hole position is set to the maximum value of the operating angle variable range according to the variable valve mechanism 20, the variable valve apparatus 1 according to the first embodiment of the present invention can shorten this operation time T2.

To generate a sufficient swirl flow, it is effective to make even greater the difference in the lift between the first valve 16L and the second valve 16R. Accordingly, the operating angle posture of the first rocking cam arm 40L to be controlled to achieve such a desired swirl flow after the pin coupling is substantially small. In the variable valve apparatus 1 according to the first embodiment of the present invention, the position of the pin hole 80 is set, as described above, so as to allow a pin switching operation to be performed at the smallest operating angle of the range requiring the pin switching operation. It is therefore possible to change the operating angle posture of the first rocking cam arm 40L quickly to the target, sufficiently small operating angle posture. Specifically, it is possible to shorten the operation time T2 even more effectively.

Correspondence between elements of the first embodiment of the present invention and those in some aspects of the present invention is as follows. Specifically, the first valve 16L in the first embodiment corresponds to the “valve to be switched” in the first aspect of the present invention; the rocking cam arm 40 in the first embodiment corresponds to the “rocking member” in the first aspect of the present invention; the control shaft 34, the control arm 36, the link arm 38, the first roller 42, the second roller 44, and the slide surface 50 in the first embodiment correspond to the “valve-opening characteristics variable means” in the first aspect of the present invention; the large lift arm 70 in the first embodiment correspond to the “valve-opening characteristics fixing means” in the first aspect of the present invention; and the arm coupling mechanism 72 in the first embodiment corresponds to the “changing means” in the first aspect of the present invention, respectively.

Similarly, the first roller 42 and the second roller 44 in the first embodiment correspond to the “intermediate member” in the third aspect of the present invention; the control shaft 34, the control arm 36, and the link arm 38 in the first embodiment correspond to the “control means” in the third aspect of the present invention; the second driving cam 14 in the first embodiment corresponds to the “second cam” in the third aspect of the present invention; and the large lift arm 70 in the first embodiment corresponds to the “input arm” in the third aspect of the present invention, respectively.

Second Embodiment

A second embodiment of the present invention will be described below with reference to FIGS. 5 through 8.

FIG. 5 is a view for illustrating the arrangement of a variable valve apparatus 90 according to the second embodiment of the present invention. The variable valve apparatus 90 according to the second embodiment of the present invention has the same arrangements as those of the variable valve apparatus 1 according to the first embodiment of the present invention, except for the arrangement of a camshaft 92. Specifically, in the variable valve apparatus 90, too, the position of a pin hole 80 is set so that the pin switching operation can be executed when a second rocking cam arm 40R is in a posture for achieving an operating angle for the operating range required for the switching operation (pin switching operation) from the double valve variable control to the single valve variable control.

Referring to FIG. 5, the variable valve apparatus 90 has the same arrangement as that of the first embodiment, wherein a second driving cam 96 has a cam height greater than the cam height of a first driving cam 94. Further, the first driving cam 94 is mounted on the camshaft 92 at an angle different from the second driving cam 96 on the camshaft 92. Specifically, the second driving cam 96 is fixed to the camshaft 92 at a position deviated by a predetermined angle α on the advance side relative to the first driving cam 94.

FIG. 6 is a diagram showing valve-opening characteristics of a valve 16 achieved by the variable valve apparatus 90. In accordance with the arrangement of the variable valve apparatus 90 described above, a valve-opening time of a second valve 16R driven by the second driving cam 96 can be advanced relative to a variably controlled valve-opening time of a first valve 16L so that given valve-opening characteristics can be achieved through a large lift arm 70 and the second rocking cam arm 40R during the single valve variable control. According to such settings made for the camshaft 92, the first valve 16L controlled to offer a small operating angle can be opened after a vacuum develops in a cylinder by the opening of the second valve 16R at first. This increases the flow velocity of an intake when the first valve 16L on the small operating angle side opens, allowing an effective swirl flow to be generated. Such an effect can be achieved without using a mechanism (VVT mechanism) for varying the phase of the valve 16.

In accordance with the second embodiment of the present invention, it is arranged that the second driving cam 96 is fixed to the camshaft 92 at the position deviated by the predetermined angle a on the advance side relative to the first driving cam 94. The technique adopted to vary the phase of the two cams is not limited to this in the present invention. FIG. 7 is a view for illustrating the arrangement of such a modified example. In a variable valve apparatus 100 shown in FIG. 7, unlike the variable valve apparatus 90 shown in FIG. 5, a first driving cam 102 is fixed at a position deviated by a predetermined angle β on the advance side relative to a second driving cam 104.

FIG. 8 is a diagram showing valve-opening characteristics of a valve 16 achieved by the variable valve apparatus 100. In accordance with the arrangement of the variable valve apparatus 100 described above, a valve-opening time of a first valve 16L variably controlled by a variable valve mechanism 20 can be advanced relative to a valve-opening time of a second valve 16R driven by a fixed valve mechanism 30 during the single valve variable control. According to such settings made for a camshaft 106, a pumping loss can be effectively reduced by first opening the first valve 16L before a vacuum develops in a cylinder. Such an effect can be achieved without using a mechanism (VVT mechanism) for varying the phase of a valve 16.

Third Embodiment

A third embodiment of the present invention will be described below with reference to FIGS. 9 through 11(A) and 11(B).

A variable valve apparatus 110 according to the third embodiment of the present invention has the same arrangements as those of the variable valve apparatus 1 according to the first embodiment of the present invention, except for the following two points. Specifically, the posture is different of a second rocking cam arm 40R when the switching operation (pin switching operation) from the double valve variable control to the single valve variable control is performed. Further, a second driving cam 114 differs in height from a first driving cam 112.

FIG. 9 shows a torque curve diagram for illustrating the operating range, in which the single valve variable control is executed, in the variable valve apparatus 110 according to the third embodiment of the present invention. Referring to FIG. 9, the double valve variable control, in which both valves are set to achieve a large operating angle, is executed in a heavy load, high speed range. In ranges other than the heavy load, high speed range, the single valve variable control, in which only a first valve 16L is varied to offer a small operating angle, is executed. In the first embodiment as described earlier, it is arranged that the pin switching operation is executed on the side of the smallest operating angle of the range, over which such a single valve variable control is executed. The variable valve apparatus 110 according to the third embodiment of the present invention, on the other hand, is characterized in that the pin switching operation is performed on the side of the greatest operating angle of the range, over which such a single valve variable control is executed.

FIGS. 10(A) and 10(B) are views for illustrating problems as they are posed when the pin switching operation is performed on the side of the small operating angle of the range, over which the single valve variable control is executed. FIG. 10(A) is a view showing a condition, in which a second roller 44 in contact with a rocking cam arm 40 is located on a leading end side of the rocking cam arm 40, i.e., a small operating angle control state. FIG. 10(B) is a view showing a condition, in which the pin switching operation is performed in the condition shown in FIG. 10(A) to set the single valve variable control state and then a control shaft 34 is rotated to move a second roller 44 toward the axial center of the control shaft 34, i.e., a large operating angle control state. In the condition shown in FIG. 10(B), there is produced a gap between a second driving cam 14 on the side of a fixed operating angle and an input roller 74. This is because of the following reason. Specifically, a second rocking cam arm 40R and a large lift arm 70 are coupled together using a pin 76 in the condition shown in FIG. 10(A); a second roller 44 then moves to change the posture of the second rocking cam arm 40R, which results in a changed posture of the large lift arm 70. A gap thus produced between the second driving cam 14 and the input roller 74 causes the second driving cam 14 to contact the input roller 74 repeatedly at each lift motion. As a result, noise or impact load occurs during contact.

FIGS. 11(A) and 11(B) are views for illustrating operations when the setting is made for pin switching operation according to the third embodiment of the present invention. FIG. 11(A) is a view showing a condition, in which the second roller 44 is located at a position that results in the greatest operating angle of the region of the single valve variable control. In accordance with the third embodiment of the present invention, the second rocking cam arm 40R includes a pin hole 116 disposed therein so that the pin switching operation can be performed in this condition as described above. FIG. 11(B) is a view showing a condition, in which the pin switching operation is performed in the condition shown in FIG. 11(A) to set the single valve variable control state and then the control shaft 34 is rotated to move the second roller 44 toward the leading end side of the rocking cam arm 40, i.e., a small operating angle control state. In the condition shown in FIG. 11(B), a first rocking cam arm 40L on the variable operating angle side is kept in contact with the second roller 44; however, a gap is produced between the second rocking cam arm 40R on the fixed operating angle side and the second roller 44 when the second roller 44 moves in a direction of being away from the control shaft 34.

As described in the foregoing, according to the setting made in the third embodiment of the present invention, the single valve variable control is executed at all times on the side of an operating angle smaller than that at which the pin switching operation is performed. Accordingly, there is produced a gap between the second rocking cam arm 40R and the second roller 44 during the single valve variable control; however, since there is no gap produced between the second driving cam 14 and the input roller 74, unlike the arrangement shown in FIGS. 10(A) and 10(B), noise or impact load is not generated during lift motion.

Fourth Embodiment

A fourth embodiment of the present invention will be described below with reference to FIGS. 12 through 17.

FIG. 12 is a view for illustrating the arrangement of a variable valve apparatus 120 according to the fourth embodiment of the present invention. Referring to FIG. 12, the variable valve apparatus 120 according to the fourth embodiment of the present invention has the same arrangements as those of the variable valve apparatus 1 according to the first embodiment of the present invention except in the following points. Specifically, a first driving cam 12 for moving the first roller 42 has the same profile as that of a second driving cam 122 for moving the input roller 74. Further, an arm coupling mechanism 124 has a different arrangement from that of the counterpart in the first embodiment of the present invention.

More specifically, in the arm coupling mechanism 124 according to the fourth embodiment of the present invention, an axis of a pin 76 is aligned with an axis of a pin hole 128 when a second rocking cam arm 126R is brought into a posture that achieves the greatest operating angle. FIG. 12 shows a condition, in which the second rocking cam arm 126R is in a posture that achieves the maximum operating angle less a predetermined value relative to the pin hole 128 arranged as described above. Specifically, FIG. 12 shows a condition, in which the pin 76 is axially misaligned with the pin hole 128. The fourth embodiment of the present invention is characterized in that the arm coupling mechanism 124 is allowed to perform the pin switching operation in the condition as shown in FIG. 12.

FIG. 13 is a cross-sectional view for illustrating the arrangement specific to the arm coupling mechanism 124 according to the fourth embodiment of the present invention. Whereas the hydraulic chamber 78 is disposed on the side of the large lift arm 70 in the arrangement shown in FIG. 3, it is assumed that a hydraulic path 132 and a hydraulic chamber 134 are disposed on the side of, not a large lift arm 130, but the second rocking cam arm 126R in the fourth embodiment. It is further assumed that the side of the large lift arm 130 includes the pin hole 128 that accommodates a piston 136 and a return spring 138. The arm coupling mechanism 124 according to the fourth embodiment of the present invention is characterized in the shape of a portion marked with “A” in FIG. 13 in the pin hole 128 in the large lift arm 130.

FIGS. 14(A) and 14(B) are enlarged views showing the portion A of FIG. 13. More specifically, FIG. 14(A) is a view showing the pin hole 128 as viewed from the side of the hydraulic chamber 134. FIG. 14(B) is a view showing a cross section of the portion A. Referring to FIGS. 14(A) and 14(B), a guide surface 128 a for guiding the pin 76 is formed at an entrance of the pin hole 128. The guide surface 128 a is formed such that a more largely recessed radius is formed at a portion thereof on the side (on the right in FIG. 14(B)), on which the second rocking cam arm 126R moves in for pin switching operation, thereby ensuring that the pin 76 is more easily inserted in the pin hole 128. The guide surface 128 a is formed into a radius shape having a gradually greater radius toward the entrance of the pin hole 128. More specifically, the guide surface 128 a is formed such that an inclined angle relative to an axis of the pin hole 128 is gradually smaller toward the entrance of the pin hole 128. These arrangements of the arm coupling mechanism 124 can be achieved similarly even in the arrangement having the hydraulic chamber 78 on the side of the large lift arm 70 (the arrangement shown in FIG. 3), if a guide surface similar to the guide surface 128 a is disposed on the side of the second rocking cam arm 40R.

FIGS. 15(A) and 15(B) are views for illustrating pin switching operations in the fourth embodiment of the present invention. FIG. 15(A) is a view showing a condition, in which the pin 76 is axially misaligned with the pin hole 128. In accordance with the arm coupling mechanism 124 according to the fourth embodiment of the present invention, even when the pin 76 is axially misaligned with the pin hole 128, the pin 76 to which a hydraulic pressure has been supplied is guided onto the guide surface 128 a, which rotates the second rocking cam arm 126R to bring the pin 76 into axial alignment with the pin hole 128 as shown in FIG. 15(B). This allows the pin 76 to be inserted into the pin hole 128.

FIG. 16 is a view for illustrating the operation of the second rocking cam arm 126R during the pin switching operation. The above-referenced FIG. 12 is associated with the condition of FIG. 15(A). In accordance with the arm coupling mechanism 124 according to the fourth embodiment of the present invention as described heretofore, the pin switching operation can be performed even when the pin 76 is axially misaligned with the pin hole 128 as shown in FIG. 12. FIG. 16 shows a condition, in which the pin switching operation is completed as a result of rotation of the second rocking cam arm 126R as shown in FIG. 15(B) after an attempt has been made of a pin switching operation in the condition shown in FIG. 12. Specifically, through such a pin switching operation, the second rocking cam arm 126R, which is in the same posture as the first rocking cam arm 40L before the start of the pin switching operation, rotates to the position shown in FIG. 16 as the pin 76 is inserted into the pin hole 128.

As described in the foregoing, the arrangements made in the fourth embodiment of the present invention eliminate the need for driving the control shaft 34 to thereby move the second rocking cam arm 126R to an operating angle posture, in which the pin 76 is axially aligned with the pin hole 128, for execution of the pin switching operation. Specifically, the operation time can be reduced for moving the second rocking cam arm 126R into the operating angle posture that enables the pin switching operation when a need arises for single valve variable control. In addition, according to the arrangements made in the fourth embodiment of the present invention, the second rocking cam arm 126R itself rotates to a position resulting in the maximum operating angle, at which the pin 76 is coupled. This eliminates the need for arranging to make the second driving cam 122 have a cam height greater than that of the first driving cam 12 as in the first and second embodiments described earlier. It should, however, be noted that, in the arrangements made in the fourth embodiment of the present invention, too, the second driving cam 122 may be arranged to have a cam height different from that of the first driving cam 12.

In the arrangements of the arm coupling mechanism 124 described above, the guide surface 128 a is formed into a radius shape having a gradually greater radius toward the entrance of the pin hole 128. Accordingly, when the single valve variable control is switched to the double valve variable control, i.e., when the pin 76 moves out of the pin hole 128, the speed, at which the second rocking cam arm 126R moves toward the small operating angle side with the pin 76, can be gradually reduced through the effect of the shape of the guide surface 128 a as shown in FIG. 17. As a result, when the second rocking cam arm 126R contacts again with the second roller 44 upon release of the coupling of the pin 76, the contact can be made mild, thus contributing to a reduced noise or impact load during contact.

In the fourth embodiment of the present invention, the guide surface 128 a in the pin hole 128 is formed into a radius. The shape of the guide surface according to the present invention is not limited to the radius. For example, the guide surface may be chamfered in a number of steps such that the inclined angle relative to the axis of the pin hole is smaller toward the entrance of the pin hole.

The guide surface 128 a in accordance with the fourth embodiment of the present invention corresponds to the “guide surface” in the sixth aspect of the present invention. 

1-8. (canceled)
 9. A variable valve apparatus in which control on valve-opening characteristics of at least one valve to be switched of a plurality of valves is changed from that under a variable control mode to that under a fixed control mode or vice versa, the variable valve apparatus comprising: a rocking member interposed between a main cam and the valve, the rocking member transmitting a pressing force of the main cam to the valve; valve-opening characteristics variable means for controlling a posture of the rocking member within a predetermined range to variably control valve-opening characteristics of the valve to be switched; valve-opening characteristics fixing means for fixedly controlling the valve-opening characteristics of the valve to be switched; and changing means for switching control on the valve-opening characteristics of the valve to be switched from that under the variable control mode to that under the fixed control mode or vice versa; wherein the changing means allows the valve-opening characteristics of the valve to be switched to be changed in a posture of the rocking member associated with an operating range requiring a switch of the valve-opening characteristics of the valve to be switched.
 10. The variable valve apparatus according to claim 9, wherein an operating range requiring a switch of the valve-opening characteristics of the valve to be switched includes a low engine speed range or a light load range for reduced NOx or improved fuel economy.
 11. The variable valve apparatus according to claim 9, wherein the valve-opening characteristics variable means includes an intermediate member disposed between the main cam and the valve to be switched and control means for changing a position of the intermediate member; wherein the intermediate member is shared among the plurality of valves including the valve to be switched; including a second cam that is separate from the main cam; wherein the valve-opening characteristics fixing means includes an input arm that rocks in phase with rotation of the second cam; wherein the changing means engages or disengages coupling between the rocking member for moving the valve to be switched and the input arm; and wherein the second cam is configured to have a greater cam height than the main cam.
 12. The variable valve apparatus according to claim 11, wherein the changing means is configured such that, when the operating range requiring a switch of the valve-opening characteristics of the valve to be switched exists over a predetermined range, the valve-opening characteristics of the valve to be switched can be switched with the rocking member in a posture that achieves the minimum operating angle and/or lift of the valve to be switched within the predetermined range.
 13. The variable valve apparatus according to claim 11, wherein the changing means is configured such that, when the operating range requiring a switch of the valve-opening characteristics of the valve to be switched exists over a predetermined range, the valve-opening characteristics of the valve to be switched can be switched with the rocking member in a posture that achieves the maximum operating angle and/or lift of the valve to be switched within the predetermined range.
 14. The variable valve apparatus according to claim 9, wherein the valve-opening characteristics variable means includes an intermediate member disposed between the main cam and the valve to be switched and control means for changing a position of the intermediate member; wherein the intermediate member is shared among the plurality of valves including the valve to be switched; including a second cam that is separate from the main cam; wherein the valve-opening characteristics fixing means includes an input arm that rocks in phase with rotation of the second cam; wherein the changing means includes a pin, the changing means engaging or disengaging coupling of the pin between the rocking member for moving the valve to be switched and the input arm; wherein either the rocking member for moving the valve to be switched or the input arm includes a pin hole, in which the pin is inserted; and wherein an entrance portion of the pin hole includes a guide surface formed for guiding the pin being inserted into, or moved out of, the pin hole.
 15. The variable valve apparatus according to claim 14, wherein the guide surface has an inclined angle relative to an axis of the pin hole, the angle becoming smaller toward an entrance portion of the pin hole.
 16. The variable valve apparatus according to claim 11, wherein a profile of the second cam is configured such that the second cam achieves a phase of the valve to be switched different from a valve phase achieved by the main cam.
 17. A variable valve apparatus in which control on valve-opening characteristics of at least one valve to be switched of a plurality of valves is changed from that under a variable control mode to that under a fixed control mode or vice versa, the variable valve apparatus comprising: a rocking member interposed between a main cam and the valve, the rocking member transmitting a pressing force of the main cam to the valve; valve-opening characteristics variable means for controlling a posture of the rocking member within a predetermined range to variably control valve-opening characteristics of the valve to be switched; valve-opening characteristics fixing means for fixedly controlling the valve-opening characteristics of the valve to be switched; and changing means for switching control on the valve-opening characteristics of the valve to be switched from that under the variable control mode to that under the fixed control mode or vice versa; wherein the changing means allows the valve-opening characteristics of the valve to be switched to be changed in a posture of the rocking member associated with an operating range requiring a switch of the valve-opening characteristics of the valve to be switched; wherein the operating range requiring a switch of the valve-opening characteristics of the valve to be switched is an operating range, in which an operating angle of the valve to be switched is substantially 100 to 200° C.A.
 18. A variable valve apparatus in which control on valve-opening characteristics of at least one valve to be switched of a plurality of valves is changed from that under a variable control mode to that under a fixed control mode or vice versa, the variable valve apparatus comprising: a rocking member interposed between a main cam and the valve, the rocking member transmitting a pressing force of the main cam to the valve; valve-opening characteristics variable means for controlling a posture of the rocking member within a predetermined range to variably control valve-opening characteristics of the valve to be switched; valve-opening characteristics fixing means for fixedly controlling the valve-opening characteristics of the valve to be switched; and changing means for switching control on the valve-opening characteristics of the valve to be switched from that under the variable control mode to that under the fixed control mode or vice versa; wherein the changing means allows the valve-opening characteristics of the valve to be switched to be changed in a posture of the rocking member associated with an operating range requiring a switch of the valve-opening characteristics of the valve to be switched; wherein the valve-opening characteristics variable means includes an intermediate member disposed between the main cam and the valve to be switched and control means for changing a position of the intermediate member; wherein the intermediate member being shared among the plurality of valves includes the valve to be switched; including a second cam that is separate from the main cam; wherein the valve-opening characteristics fixing means includes an input arm that rocks in phase with rotation of the second cam; wherein the changing means includes a pin, the changing means engaging or disengaging coupling of the pin between the rocking member for moving the valve to be switched and the input arm; wherein either the rocking member for moving the valve to be switched or the input arm includes a pin hole, in which the pin is inserted; and wherein an entrance portion of the pin hole includes a guide surface formed for guiding the pin being inserted into, or moved out of, the pin hole.
 19. The variable valve apparatus according to claim 18, wherein an operating range requiring a switch of the valve-opening characteristics of the valve to be switched includes a low engine speed range or a light load range for reduced NOx or improved fuel economy.
 20. The variable valve apparatus according to claim 18, wherein the guide surface has an inclined angle relative to an axis of the pin hole, the angle becoming smaller toward an entrance portion of the pin hole.
 21. The variable valve apparatus according to claim 18, wherein a profile of the second cam is configured such that the second cam achieves a phase of the valve to be switched different from a valve phase achieved by the main cam.
 22. A variable valve apparatus in which control on valve-opening characteristics of at least one valve to be switched of a plurality of valves is changed from that under a variable control mode to that under a fixed control mode or vice versa, the variable valve apparatus comprising: a rocking member interposed between a main cam and the valve, the rocking member transmitting a pressing force of the main cam to the valve; valve-opening characteristics variable means for controlling a posture of the rocking member within a predetermined range to variably control valve-opening characteristics of the valve to be switched; valve-opening characteristics fixing means for fixedly controlling the valve-opening characteristics of the valve to be switched; changing means for switching control on the valve-opening characteristics of the valve to be switched from that under the variable control mode to that under the fixed control mode or vice versa; and a second cam that is separate from the main cam; wherein the changing means allows the valve-opening characteristics of the valve to be switched to be changed in a posture of the rocking member associated with an operating range requiring a switch of the valve-opening characteristics of the valve to be switched; wherein a profile of the second cam is configured such that the second cam achieves a phase of the valve to be switched different from a valve phase achieved by the main cam.
 23. A variable valve apparatus in which control on valve-opening characteristics of at least one valve to be switched of a plurality of valves is changed from that under a variable control mode to that under a fixed control mode or vice versa, the variable valve apparatus comprising: a rocking member interposed between a main cam and the valve, the rocking member transmitting a pressing force of the main cam to the valve; a valve-opening characteristics variable unit for controlling a posture of the rocking member within a predetermined range to variably control valve-opening characteristics of the valve to be switched; a valve-opening characteristics fixing unit for fixedly controlling the valve-opening characteristics of the valve to be switched; and a changing unit for switching control on the valve-opening characteristics of the valve to be switched from that under the variable control mode to that under the fixed control mode or vice versa; wherein the changing unit allows the valve-opening characteristics of the valve to be switched to be changed, in a condition, in which the rocking member is controlled by the valve-opening characteristics variable unit so that the rocking member is in a posture that is associated with an operating range requiring a switch of the valve-opening characteristics of the valve to be switched and excepts a posture for achieving a maximum or minimum value in the variable range of operating angle and/or lift of the valve to be switched.
 24. A variable valve apparatus in which control on valve-opening characteristics of at least one valve to be switched of a plurality of valves is changed from that under a variable control mode to that under a fixed control mode or vice versa, the variable valve apparatus comprising: a rocking member interposed between a main cam and the valve, the rocking member transmitting a pressing force of the main cam to the valve; a valve-opening characteristics variable unit for controlling a posture of the rocking member within a predetermined range to variably control valve-opening characteristics of the valve to be switched; a valve-opening characteristics fixing unit for fixedly controlling the valve-opening characteristics of the valve to be switched; and a changing unit for switching control on the valve-opening characteristics of the valve to be switched from that under the variable control mode to that under the fixed control mode or vice versa; wherein the changing unit allows the valve-opening characteristics of the valve to be switched to be changed in a posture of the rocking member associated with an operating range requiring a switch of the valve-opening characteristics of the valve to be switched; wherein the operating range requiring a switch of the valve-opening characteristics of the valve to be switched is an operating range, in which an operating angle of the valve to be switched is substantially 100 to 200° C.A.
 25. A variable valve apparatus in which control on valve-opening characteristics of at least one valve to be switched of a plurality of valves is changed from that under a variable control mode to that under a fixed control mode or vice versa, the variable valve apparatus comprising: a rocking member interposed between a main cam and the valve, the rocking member transmitting a pressing force of the main cam to the valve; a valve-opening characteristics variable unit for controlling a posture of the rocking member within a predetermined range to variably control valve-opening characteristics of the valve to be switched; a valve-opening characteristics fixing unit for fixedly controlling the valve-opening characteristics of the valve to be switched; and a changing unit for switching control on the valve-opening characteristics of the valve to be switched from that under the variable control mode to that under the fixed control mode or vice versa; wherein the changing unit allows the valve-opening characteristics of the valve to be switched to be changed in a posture of the rocking member associated with an operating range requiring a switch of the valve-opening characteristics of the valve to be switched; wherein the valve-opening characteristics variable unit includes an intermediate member disposed between the main cam and the valve to be switched and a control unit for changing a position of the intermediate member; wherein the intermediate member is shared among the plurality of valves including the valve to be switched; including a second cam that is separate from the main cam; wherein the valve-opening characteristics fixing unit includes an input arm that rocks in phase with rotation of the second cam; wherein the changing unit includes a pin, the changing unit engaging or disengaging coupling of the pin between the rocking member for moving the valve to be switched and the input arm; wherein either the rocking member for moving the valve to be switched or the input arm includes a pin hole, in which the pin is inserted; and wherein an entrance portion of the pin hole includes a guide surface formed for guiding the pin being inserted into, or moved out of, the pin hole.
 26. A variable valve apparatus in which control on valve-opening characteristics of at least one valve to be switched of a plurality of valves is changed from that under a variable control mode to that under a fixed control mode or vice versa, the variable valve apparatus comprising: a rocking member interposed between a main cam and the valve, the rocking member transmitting a pressing force of the main cam to the valve; a valve-opening characteristics variable unit for controlling a posture of the rocking member within a predetermined range to variably control valve-opening characteristics of the valve to be switched; a valve-opening characteristics fixing unit for fixedly controlling the valve-opening characteristics of the valve to be switched; a changing unit for switching control on the valve-opening characteristics of the valve to be switched from that under the variable control mode to that under the fixed control mode or vice versa; and a second cam that is separate from the main cam; wherein the changing unit allows the valve-opening characteristics of the valve to be switched to be changed in a posture of the rocking member associated with an operating range requiring a switch of the valve-opening characteristics of the valve to be switched; wherein a profile of the second cam is configured such that the second cam achieves a phase of the valve to be switched different from a valve phase achieved by the main cam. 